The present invention relates to a bearing device for a turbocharger and more particularly a bearing device for a turbocharger which can ensure stable rotation of a turbine shaft without adversely affecting the floating condition of an oil film damper.
FIG. 1 shows a conventional bearing device for a turbocharger. Reference numeral 1 designates a turbine casing; 2, a compressor casing; 3, a bearing casing between the casings 1 and 2; 4, a heat shielding plate; 5, a bearing housing disposed in the bearing casing 3; 6, a turbine shaft; 7, a turbine wheel; 8, an oil thrower spacer; 9, an oil thrower; 10, a compressor wheel; 11, a ball bearing on the side of the turbine; 12, a ball bearing on the side of the compressor; 13, an oil film damper on the side of the turbine which is disposed within the bearing housing 5 in a floating state through an oil film so as to support the ball bearing 11 on the side of the turbine; 14, a compressor-side oil film damper which is also disposed in the bearing housing 5 in a floating state through an oil film so as to support the compressor-side ball bearing 12; 15, a coiled spring interposed between the dampers 13 and 14 so that the outer races of the oil bearings 11 and 12 are moved away from each other; 16, a damper retainer; 17, a bearing spacer; 18, an oil inlet; 19, an oil outlet; 20, a water jacket; and 21 and 22, retaining rings to be described in detail hereinafter.
As described above, the conventional oil film dampers are of the split type; that is, the turbine-side oil film damper 13 and the compressor-side oil film damper 14 are disposed independently of each other. Though supported by the coiled spring 15, the oil film dampers 13 and 14 can move independently of each other so that there arises the problem that the stability in rotation of the turbine shaft 6 is decreased. Especialy when the clearances between the dampers 13 and 14 on the one hand and the bearing housing 5 on the other hand are large, the oil film dampers 13 and 14 tend to rotate easily so that the stability in rotation of the turbine shaft 6 is further decreased. Furthermore the coiled spring 15 must be preloaded to provide a force greater than the thrust of the turbine bearing so that when the thrust is exerted on the turbine or the compressor, the ball bearing 11 or 12 is prevented from being pushed into the oil film damper 13 or 14. When the force of the coiled spring 15 exerted on the dampers 13 and 14 becomes greater, the life of the ball bearings 11 and 12 is considerably shortened. Furthermore there is the problem that since the coiled spring 15 is very strong, the assembling and mechanical efficiency is remarkably decreased. It is not preferable that the stopper rings 21 and 22 are disposed and engaged with the inner end faces of the dampers 13 and 14 in order to decrease the force of the coiled spring 15 because the dampers 13 and 14 rotate in unison with the bearing shaft 6.
In the view of the above, the primary object of the present invention is to provide a bearing device for a turbocharger which can decrease the preload of the spring so that the life of the ball bearings can be increased; which can minimize mechanical losses because of the ball bearings; which can reduce turbo lag; which can interrupt the rotation of the oil film dampers so that the stability in rotation of the turbine shaft can be improved and the discharge of working oil can be facilitated, whereby the mechanical losses can be minimized; and which is simple in construction so that the fabrication of the bearing device is much facilitated.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.